🎨 Allow repeated `memref.load`s of the same qubit

[denialhaag]

Currently, the QCProgramBuilder does not allow repeated memref.loads of the same qubit:

core/mlir/lib/Dialect/QC/Builder/QCProgramBuilder.cpp

Lines 162 to 170 in def69f1

	if (regionStack.size() == 1) {
	llvm::reportFatalUsageError(
	"Qubit cannot be loaded in the main function region");
	}
	for (Region* curr : regionStack) {
	if (loadedQubits[curr][memref].contains(index)) {
	llvm::reportFatalUsageError("Qubit already loaded in enclosing region");
	}
	}

We should look into whether we can relax this. MLIR might have built-in canonicalization patterns that remove redundant memref.loads.

This change would also allow us to simplify the translation from OpenQASM 3 to QC. For some more details, see #1862 (comment) and the comments below.